Power controlling arrangement for duplex transmission

Abstract: The present invention relates to an arrangement (20) for duplex transmission in a radio or similar with transmitter (1) and receiver (2), the arrangement compriseing a transmitter filter (3), receiver filter (4) and preferably a transmitter/receiver device (5), wherein the receiver filter (4) comprises a so called SAW-filter (Surface Acoustic Wave Filter) and the transmitter filter (3) and the SAW-filter (4) are connected via a circulator (6). The arrangement comprises a power detecting device (7) for detecting the power in/to the receiver filters (SAW-filters) and the power detecting arrangement (7) provides a feed-back signal to a controlling arrangement for controlling the power our from a power amplifier (8) arranged in front of the transmitter filter (3).

Description: Technical field The present invention relates to an arrangement for duplex transmission in a radio or similar with transmitter and receiver wherein the arrangement comprises a transmitter filter, a receiver filter and preferably a transmitter/receiver device which is fixedly or demountably arranged, wherein the receiver filter comprises a SAW-filter (Surface Acoustic Wave filter) and the transmitter filter and the SAW-filter are connected via a cirulator. The filters of a such an arrangement, on which the requirements are high i.e. as far as selectivity, through attenuation etc. is concerned, are today large among others because of physically large resonators. Therethrough arrangements of the given kind are difficult to integrate due their size which can be both time-consuming as well as it leads to increased costs. Furthermore, the products comprising said arrangement are large and cumbersome which can be of great significance for the intended application as well as its use and utilization as such. An example where it is significant that the size of such arrangements can be limited are hand-held telephones, particularly so called analogue cellular pocket telephones. State of the art Arrangements as referred to above are known. According to a know embodiment a duplex filter is arranged between a transmitter and a receiver which comprises a receiver filter and a transmitter filter wherein between the filters an antenna is arranged. With known embodiments either ceramic filters or "helical" filters are used as transmitter filters as well as receiver filters. Those filters however, have physically large resonators why the arrangement of the component will get large and difficult to integrate in customer specific circuits such as for example ASIC (Application Specific Integrated Circuit). These arrangements are used in among others analogue cellular hand-held telephones which also will be large among others since the duplex filters are large. It is a drawback in portable telephones since it is essential that these are small and easy to handle in order to become really customer friendly. The requirements of the market get higher and higher in respect thereof. Even if also other factors play a roll, such as e.g. batteries, involved electronic etc., the filter size is a very important factor. The patent document US-A-4 811 421 discloses a transmitting and receiving station in which the power transmitted is controlled as a function of power received. Furthermore, the patent document US-A-4 792 939 discloses a transceiver comprising a coupler circuit for transmission power control. Summary of the invention The object with the present invention is to provide an arrangement for duplex transmission in a radio or similar with transmitter and receiver as stated above which is physically small, easy to integrate at the same time as it fulfils high requirements as to a high selectivity, low through attenuation, a high Q etc. Particulary the object with the arrangement is to attenuate transmitted power into the receiver to avoid that this gets blocked, to attenuate noise from the transmitter into the receiver on the receiving frequency, to attenuate overtones from transmitter to antenna, to attenuate local oscillator frequency from receiver to antenna, to attenuate image frequencies into the receiver from the antenna, to attenuate frequencies which may cause intermodulation in the transmitter and arrive at the receiver frequency, arrange for the through attenuate on transmitting frequency from transmitter to antenna is low as well as to provide that the through attenuate on receiving frequency from antenna to transmitter is low, which however are normal requirements on duplex filters. The object with the invention is further to provide that more or less the same requirements and performance can be fulfilled as with known duplex filters with a considerably smaller surface and the volume respectively of the arrangement. It is furthermore an object with the invention to provide an arrangement which is simple and cheap to fabricate at the same time as the performance is good and which is easy to handle and which is small. An arrangement through which these as well as other objects are achieved is provided through an arrangement as initially stated which comprises a power detecting arrangement for detecting and measuring the power in to the receiver filter or the SAW-filter, said power detecting arrangement providing a feed-back signal to a controlling arrangement for controlling the power out from a power amplifier arranged in front of the transmitter filter. Preferred embodiments are given through the characteristics of the subclaims. According to one embodiment the transmitter filter may comprise a conventional so called ceramic filter but may also comprise a so called helical filter. The power detecting device may particularly comprise between the circulator and the SAW-filter arranged detecting means. The power detecting device particularly comprises at least one directional coupler. According to a preferred embodiment the detecting means arranged between the circulator and the SAW-filter comprises a directional coupler. Particularly the power detecting device may comprise a first directional coupler arranged between the circulator and the SAW-filter and a second directional coupler arranged in front of the transmitter filter. According to an alternate embodiment the power detecting device may comprise a first directional coupler arranged between the circulator and the SAW-filter and a second directional coupler arranged between the transmitter filter and the circulator. The power amplifier is arranged in front of the transmitter and advantageously a second directional coupler is arranged between the power amplifier and the transmitter filter. The power detecting device is advantageously connected to a power regulator for controlling the transmitter power. The power regulator particularly comprises a so called PI-regulator which controls the power out from the power amplifier. According to one embodiment of the invention the circulator has a through attenuation of approximately 0,8 dB and a reverse isolation of preferably more than 12dB. Particularly in-, and output respectively between transmitter, receiver and antenna are loaded with an impedance of approximately 50 Ω. If the attenuation from the transmitter 1 to the receiver 2 is not sufficient, the transmitted power received by the receiver filter will be to high and the receiver filter might e.g. be damaged. Therefore the power to be received by the receiver filter 4 is sensed and measured and a signal is fed back to a controlling arrangement to reduce the power from the transmitter or the power amplifier. The power can be reduced via a power regulator, the amplification in the amplifier can be reduced or separate means such as a variable attenuating means or similar can be used. The power may e.g. have to be reduced if the transmitter/receiver device (e.g. an antenna) loads the circulator too much or incorrectly, or in a non desired manner. Brief description of the drawings The invention will in the following be further described with reference to the accompanying drawings in an explanatory and by no means limiting way wherein Fig. 1 illustrates a block diagram of the arrangement, Fig. 2 illustrates a block diagram of the arrangement comprising power detection and power controlling, Fig. 3 illustrates a second embodiment of the arrangement comprising power detection and power controlling and Fig. 4 schematically illustrates interconnection of transmitter, antenna, receiver. Detailed description of the invention In Fig. 1 an arrangement 10 for duplex transmission between a transmitter 1 and a receiver 2 in a radio is illustrated. The arrangement comprises a transmitter filter 3, a receiver filter 4 and a transmitter/receiver device 5 in a form of an antenna. Generally the transmitter-/receiver device 5 could also comprise a cable or similar, not shown. The transmitter filter 3 then comprises a conventional ceramic filter but it could also be a so called helical filter or any other filter. The receiver filter however comprises a so called SAW-filter, surface wave filter (Surface Acoustic Wave Filter) which is arranged in the receiver branch. Also the transmitter filter 3 might in some cases comprise a SAW-filter, when the power is lower or more power resistant SAW-filters have been produced. The SAW-filter normally has a volume which is smaller than 1/20 of the corresponding ceramic filter or similar. In Fig. 1 is not shown any detecting and controlling arrangements, this is merely indicated by a dashed line to illustrate the feed-back loop. As is illustrated in the Figures 2 and 3, the controlling of the power out from the amplifier 8 can be provided also via separate means 10 arranged after the amplifier 8. In Fig. 4 is schematically illustrated the functioning of the circulator 6. A B C illustrate connections and according to a preferred embodiment the circulator has a through damping of approximately 0,8 dB from connection A to B, from B to C and from C to A. The reverse isolation is at least 12 dB, i.e. from connection B to A, A to C and finally from C to B. For a good functioning of the circulator all in- and outputs are loaded with an impedance of 50 Ω wherethrough the back isolation can be kept high. I Fig. 2 an advantageous embodiment is illustrated in which a power detecting device is arranged which comprises a first directional coupler 7a arranged between the circulator 6 and the receiver filter 4 and a second directional coupler 7b arranged between a power amplifier 8 and the transmitter filter 3. The detecting means, the directional couplers 7a, 7b are connected to a power regulator 9 which controls or regulates the power out from the power amplifier 8. This regulator may e.g. comprise a PI-regulator. In the case of a none-advantageous loading of the antenna, e.g. if the standing-wave ratio on connection B is to big or if the antenna 5 is completely eliminated. Then the attentuation from the transmitter 1 to the receiver 2 is to small and a too large transmitted power is received in the receiver filter 4 which therethrough in some case can be damaged. Therefore the power in to the receiver filter 4 is detected which effect the receiver filter 4 which is used for set down the power amplifier 8 if the antenna 5 loads the circulator 6 the wrong way, i.e. if the isolation in the circulator 6 is too low. Fig. 3 illustrates an arrangement corresponding to that of Fig. 2 but wherein the second detecting means 7b, which particularly may be comprised by a directional coupler, is arranged behind the transmitter filter but in front of the circulator 6. In other aspects the arrangement works in a way analog to what has been described in relation to Fig. 2. The invention shall of course not be limited to the shown embodiments but may be varied freely within the scope of the claims. For example the detecting device does not have to comprise directional couplers but also other means for power detection are possible as well as it is not necessary that the receiver and the transmitter filters respectively comprise just one filter but it is also possible with two interconnected filters even if this mostly implies that the arrangement as such will be somewhat larger as well as the PI-regulator of course may be any other kind of a regulator or separate attenuating means could be arranged behind the amplifier e.t.c. The use of the arrangement is of course not limited to so called hand-held telephones but it may be used everywhere at duplex transmission in a radio or similar, comprising transmitter and receiver, e.g. in so called cordless telephones etc.

Claims: Arrangement (10; 20; 30) for duplex transmission in a radio with transmitter (1) and receiver (2) wherein the arrangement comprises a transmitter filter (3), a receiver filter (4) and a transmitter/receiver device (5) in the form of an antenna or a cable which is fixedly or demountably arranged, wherein that the receiver filter (4) comprises a SAW-filter (Surface Acoustic Wave Filter) and that the transmitter filter (3) and the SAW-filter (4) are connected via a circulator (6), characterized in that it comprises a power detecting arrangement (7a, 7b) for detecting and measuring the power into the SAW-filter (4), wherein the power detecting arrangement (7a, 7b) provides a feed-back signal to a controlling arrangement for controlling the power out from a power amplifier (8) arranged in front of the transmitter filter (3). Arrangement according to claim 1, characterized in that the detecting arrangement (7a, 7b) is connected to the power amplifier (8). Arrangement according to claim 2, characterized in that if the power detected by the detecting arrangement (7a, 7b) is too high, the amplifier (8) is controlled so that the power out is reduced either directly or via separate controlling means. Arrangement according to claim 3, characterized in that the power detecting arrangement (7a, 7b) is connected to the power amplifier (8) via a controlling arrangement in the form of a power regulator (9) for controlling the power transmitted from the power amplifier (8) and to cause a reduction therein if it is too high, if e.g. the transmitter/receiver device (5) loads the circulator improperly or detrimentally. Arrangement according to any one of claims 1-4, characterized in that the power detecting arrangement (7a, 7b) comprises a detecting means (7a) arranged between the circulator (6) and the SAW-filter (4). Arrangement according to anyone of claims 1-4, characterized in that the power detecting arrangement (7a, 7b) comprises at least one directional coupler (7a; 7b). Arrangement according to claim 5, characterized in that the detecting means (7a) arranged between the circulator (6) and the SAW-filter (4) comprises a directional coupler. Arrangement according to any one of claims 1-4, characterized in that the power detecting arrangement (7a, 7b) comprises a first directional coupler (7a) arranged between the circulator (6) and the SAW-filter (3) and a second directional coupler (7b) arranged in front of the transmitter filter (3). Arrangement according to any one of claims 1-4, characterized in that the power detecting arrangement (7a, 7b) comprises a first directional coupler (7a) arranged between the circulator (6) and the SAW-filter (3) and a second directional coupler (7b) arranged between the transmitter filter (3) and the circulator (6). Arrangement according to claim 8, characterized in that the second directional coupler (7b) is arranged between the power amplifier (8) and transmitter filter (3). Arrangement according to claim 4, characterized in that the power regulator (9) comprises a so-called PI-regulator which controls the power out from the power amplifier (8). Arrangement according to any one of claims 1-4, characterized in that the circulator (6) has a through attenuation of approximately 0,8 dB and a reverse isolation of more than 12 dB. Arrangement according to any one of claims 1-4, characterized in that the transmitter filter (3) comprises a conventional, ceramic filter. Arrangement according to any one of claims 1-4, characterized in that the transmitter filter (3) comprises a so-called helical filter. Arrangement according to any one of claims 1-4, characterized in that in- and outputs, respectively, between transmitter, receiver and antenna, are loaded with an impedance of approximately 50 Ω.

Inventors: ANDERS LARSSON JAN, ANDERS LARSSON, JAN
Applicants: ERICSSON INC, ERICSSON INC.
Application year: 1994
Main classification: H04B1
IPC codes: H03G3, H04B1